The major objectives of this proposal are: (1) to study in detail the immune response to highly localized intrabronchial stimuli and, to determine the relative role of local production of immune effector cells versus their recruitment from the blood and systemic lymphoid tissues; (2) to establish the circulatory patterns and tissue/organ distribution of immunoblasts emerging in efferent lymph in response to localized intrapulmonary immunization; (3) to assess the role of antigen in the recruitment of sensitized lymphocytes to the lung and; (4) to evaluate the effectiveness of intraperitoneal injection as a method for inducing immune reactivity in the lung. In sheep a well defined segment of the right diaphragmatic lobe of the lung is drained exclusively by the caudal mediastinal lymph node (CMLN). Cannulation of the efferent duct of the CMLN will be used to monitor the immune response and to effectively limit the response to the immunized lung segment and the regional lymph node. Such cannulations interrupt the entry of effector cells and/or their precursors into the blood precluding the possibility of their returning to the lung. Another segment of the right lung whose lymphatic drainage is independent of the CMLN will be used for comparison by simultaneously immunizing with a similar but non-cross-reacting antigen. Immune responses will be initiated with red blood cells (horse and dog) or heat-killed suspensions of gram negative bacteria (E. coli and S. minnesota) and will be assessed using a variety of humoral and cellular assays. Radioisotopic labeling along with immunfluorescent techniques will be used to establish the intrapulmonary (and non-pulmonary) distribution of efferent lymph immunoblasts and the influence of antigen on their recruitment from the blood. These studies will contribute to the elucidation of some of the basic mechanisms underlying the development of pulmonary immune responses. It is critical to define these processes in order to better understand the evolution of immunologically mediated lung disease and to establish optimal methods of immunization. A long-term objective is to evaluate the effects of pre-existing lung disease on pulmonary host defense mechanisms including normal immune responsiveness. In this regard we have recently developed a workable model of pulmonary emphysema in sheep.